Commonly assigned U.S. Pat. No. 4,603,166, issued Jul. 29, 1986, discloses polyphthalamide compositions which, when filled with glass fibers and molded, have heat deflection temperatures at 264 psi, determined according to ASTM D-648, above about 245.degree. C. (473.degree. F.). Included are compositions comprising recurring terephthalamide and adipamide or terephthalamide, isophthalamide and adipamide units and, preferably, wherein the mole ratio of dicarboxylic acid moieties provided by the terephthalamide, isophthalamide and adipamide units is about 65-90:25-0:35-5, respectively. As disclosed therein, such compositions, including particulate- and fiber-filled compositions, exhibit desirable thermal properties including heat deflection temperature, high tensile strength and flexural modulus and are useful in various applications including preparation of molded articles, fibers, and laminates.
Commonly assigned U.S. Pat. No. 4,617,342, issued Oct. 14, 1986, and commonly assigned, U.S. Pat. No. 4,863,991 issued Sep. 5, 1989, to Poppe et al., and published European Patent Application No. 84300745.1 (Publication No. 0122688), published Oct. 24, 1984, disclose polyphthalamides which, when filled with glass fibers, have heat deflection temperatures at 264 psi, determined according to ASTM D-648, above 240.degree. C. Compositions according to U.S. Pat. No. 4,617,342 are prepared from dicarboxylic acid compounds comprising terephthalic acid and isophthalic acid compounds in a mole ratio of 80:20 to about 99:1 and diamines comprising hexamethylene diamine and trimethylhexamethylene diamine in a mole ratio of about 98:2 to about 60:40. Compositions taught in U.S. Pat. No. 4,863,991 are based on terephthalic acid and isophthalic acid compounds in a mole ratio of about 70:30 to about 99:1 and hexamethylene diamine. Such compositions have utility in various applications, the neat and fiber-filled compositions being particularly suited for molding applications.
For certain end uses it would be desirable to modify certain properties of polyphthalamides such as those described above. In particular, it would be desirable to provide polyphthalamides with improved properties such as solvent resistance, especially to alcohols, and lower moisture absorption. Reduced moisture absorption is important because it can lead to better retention of mechanical properties by articles fabricated from polyamides when exposed to wet or humid environments. Such improvements would lead not only to improved performance of products fabricated from such resins in existing end uses, but also utility in additional applications with more stringent requirements. Examples of specific applications for such polyphthalamides where the above improvements would be beneficial include many injection molding and engineering applications, such as electrical and electronic connections, pump housings, and automobile under-hood and trim parts, especially those trim pieces which come in contact with windshield washer fluid or other fluids that contain alcohols which can cause cracking.
In general, it is known that modification of polymer properties may be achieved in various ways. Modification of the molecular structure of a given composition through the use of additional monomers in polymerization can lead to desirable improvements in some properties. However, the same often are accompanied by loss of other desirable properties and use of additional monomers is not always practical due to process considerations. Addition of other materials to a polymeric composition may lead to property improvements without complicating a polymerization process; however the effects of additives often are unpredictable and, again, improvements in some properties often are achieved at the expense of other properties. Blending a given polymer with one or more other polymers may give blends with combinations of properties intermediate those of the individual components; however, processing requirements often limit the number of candidates that can be blended with a given polymer in an attempt to attain desirable property modifications and properties of a blend may or may not reflect those of its components depending on compatibility of the components with each other, reactivity thereof under blending or processing conditions and other factors.
The use of 2,6-naphthalene dicarboxylic acid in the preparation of polyamides has been reported to result in improvements in certain properties. U.S. Pat. No. 4,246,395 to Mortimer, issued Jan. 20, 1981, discloses fiber-forming polyamides consisting of 45-75 mole % hexamethylene terephthalamide units, 20-40 mole % hexamethylene isophthalamide units and 5-20 mole % units derived from certain other dicarboxylic acids and diamines, examples of which include 1,3 or 1,4-cyclohexane-bis-methylamine or dodecamethylene diamine, dodecanedioic acid, 2,6-naphthalene dicarboxylic acid, 4,4'-oxydibenzoic acid or 1,4-cyclohexane dicarboxylic acid. The resulting polyamides are said to have improved thermal properties including glass transition temperature (&gt;155.degree. C.), melting points below 320.degree. C. and better thermal stabilities. Mortimer also mentions that his polyamides can be used for molding applications.
U.S. Pat. No. 4,042,571 to Kawase et al., issued Aug. 16, 1977, discloses a process for preparing a fire retardant polyamide from at least one naphthalene dicarboxylic acid, including 2,7-naphthalene dicarboxylic acid and 2,6-naphthalene dicarboxylic acid or its amide forming derivative or a combination of the two, a halogen-substituted mono- or dicarboxylic acid and an aliphatic diamine. Kawase et al. discloses that the naphthalene dicarboxylic acid is at least 40 mole % of the total acid component. According to the patent, additional dicarboxylic acid components can be used in an amount up to 55 mole % based on the total acid component. Aliphatic dicarboxylic acids such as adipic acid and aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid are mentioned as examples of such additional acids. The acid component is polymerized with a diamine, including hexamethylene diamine. The disclosed polyamides can be formed into fibers, films and other shaped articles. In addition to enhanced fire retardancy, the disclosed compositions are said to show superior mechanical properties, chemical resistance, water resistance and thermal stability, especially when the amount of naphthalene dicarboxylic acid compound used in preparation of the composition is at least 40 mole % of the total acid component. This patent discloses that if the naphthalene carboxylic acid component is less than 40 mole % of the total acid component, the above properties are sacrificed.
U.S. Pat. No. 3,538,056 to Caldwell, issued Nov. 3, 1970, discloses high-melting linear polyamides prepared from an acid component of at least 60 mole % naphthalene dicarboxylic acid and branched chain diamines. According to the patent, these polyamides may be modified by inclusion in the acid component of up to 40 mole % of another dicarboxylic acid which may be aliphatic, aromatic or alicyclic, including isophthalic acid and terephthalic acid, and a diamine including hexamethylene diamine. Uses for these polyamides are said to include films, fibers and molded objects.
U.S. Pat. No. 4,012,365 to Moriyama et al., issued Mar. 15, 1977, discloses transparent polyamides prepared with 2,7-naphthalene dicarboxylic acid or its amide-forming derivative or a combination of the two, an aliphatic diamine component containing 4 to 13 carbon atoms and a comonomer component, which may be an aromatic dicarboxylic acid comonomer, including terephthalic, isophthalic or 2,6-naphthalene dicarboxylic acid, or a diamine component. The disclosed polyamides are said to have poor crystallinity, excellent transparency, high heat resistance and chemical resistance especially to methanol, ethanol, n- and iso-propanol. The patent requires that the 2,7-naphthalene dicarboxylic acid or its amide-forming derivative or a combination of the two account for 50 to 100 mole % of the total acid component used in preparation of the polyamides, otherwise the polyamide has a reduced melting point and becomes easily soluble in alcohols. The disclosed polyamides can be melt shaped into films and fibers according to the patent.
U.S. Pat. No. 3,674,752 to Ridgway et al., issued Jul. 4, 1972, discloses fibers with increased resistance to loss in stiffness when subjected to conditions of heat and moisture and low shrinkage when subjected to hot or boiling water. The disclosed polyamides are derived from 80-90 mole % adipic acid, 10-20 mole % 1,6 or 2,6-naphthalene dicarboxylic acid and hexamethylene diamine.
U.S. Pat. No. 3,575,935 to Elam, issued Apr. 20, 1971, discloses polyamides useful as molding plastics derived from at least one aromatic or alicyclic dicarboxylic acid, including terephthalic, isophthalic and 2,6-naphthalene dicarboxylic acids, and 4,4-dimethyl-1,7-heptanediamine or 4-methyl-4-ethyl-1,7-heptanediamine or mixtures thereof. These polyamides are said to have improved heat distortion temperatures, impact strength and clarity.
Other patents which mention the use of 2,6-naphthalene dicarboxylic acid in preparation of polyamides include the following: U.S. Pat. Nos. 3,408,334; 3,467,623; 3,505,288; 3,639,358; 4,172,938 and 4,698,414.
Although the above patents disclose polyamides prepared from 2,6-and 2,7-naphthalene dicarboxylic acid, none discloses the invented polyamide compositions comprising recurring units based on terephthalic acid, isophthalic acid and 2,6-naphthalene dicarboxylic acid and one or more aliphatic diamines, or the desirable thermal and mechanical properties together with improved alcohol resistance exhibited by such compositions. Surprisingly, polyamide compositions of the present invention have excellent solvent resistance (especially alcohol resistance) even when the naphthalene dicarboxylic acid component is only 25 mole % of the total acid component, contrary to the 40-50 mole % required by some of the patents described above.
An object of this invention is to provide an improved polyamide composition. A further object is to provide a polyphthalamide composition having utility in injection molding and other applications. A still further object of the invention is to provide polyphthalamide compositions with improved solvent resistance and less moisture absorption resulting in improved retention of mechanical properties when used in applications involving exposure to wet or humid environments or alcohols.